Device removes mercury from Nevada County reservoirs

Lance Adams, from the maintenance department of the Nevada Irrigation District, places dirt on the wheel to demonstrate removing mercury from the sediment from Lake Combie, in this 2013 archive photo. The district has been testing the equipment on a demonstration basis for the last two years.

NID demonstrates the mercury manchine on a June afternoon at Lake Combie on the Meadow Vista side of the lake. Carrie Monohan of The Sierra Fund on the left and Timothy Crough, Assistant General Manager of NID on the right explain how the machine removes mercury from Lake Combie.

Related Media

Western Nevada County is no stranger to pioneers, but a collaborative consortium of scientists, water agency officials and public policy-makers is foraying into territory of a different ilk.

The Nevada Irrigation District, in collaboration with members of the Sierra Fund and a Canadian mining company, has developed a mercury machine, a device capable of sifting mercury from the bottom of reservoirs and disposing of it in an environmentally sensitive manner.

“This is the first project of its kind and we are pioneering this technology,” said NID General Manger Remleh Scherzinger.

The machine is being used in the initial phase of NID’s Combie Reservoir Sediment and Mercury Removal Project, under way at the upstream portion of Combie Reservoir.

The modestly sized lower-elevation reservoir provides water storage capacity for NID and is fed by the Bear River, which transports water from upper elevation lakes and reservoirs such as Bowman Lake and Spaulding.

The Bear River continually deposits contaminated sediment into Combie Lake, resulting in a significant reduction in storage capacity.

Scherzinger estimates the water agency has lost about 17 percent of its 5,555 acre feet of storage capacity since the Van Giesen Dam at Combie Reservoir was built in 1928.

While most water agencies throughout the nation dredge their reservoirs to counteract the problem of lost storage, the presence of toxic substances (mainly mercury) in the sediment eliminates easy solutions for NID.

Dredging stirs up methyl mercury buried in the sediment, abetting its absorption into the food chain, which can eventually present health hazards for humans.

Enter Carrie Monohan, a full-time scientist for The Sierra Fund, a nonprofit dedicated to the exploration and remediation of toxic issues in the environment related to the profusion of mining operations that characterized California in the late 19th century.

Monohan is concerned with mercury specifically relating to the Combie Lake project; as it enters the water system, it can accumulate in fish and cause severe health issues for humans that eat the fish.

More than 26 million pounds of mercury were used by miners during the California Gold Rush and an estimated 10 million pounds were left behind in the environment, Monohan said.

NID contracted with Monohan to address the problem of mercury in the reservoir and together they formulated a solution, leveraging a grant from the Sierra Nevada Conservancy to explore the vanguard of mercury removal technology.

“We are attempting to remove sediment to return the reservoirs back to their original capacity in an environmentally sensitive manner,” Scherzinger said.

NID has a lease-to-buy contract with Pegasus Earth Sensing Corporation — an Alberta, Canada-based company — for ownership of what NID is calling the mercury machine.

“It’s one of a kind,” Scherzinger said.

The mercury extraction contraption uses a specialized centrifuge to separate mercury, gold and other heavy materials from the aggregate sediment on the reservoir floor.

Monohan said the machine effectively removes 93 percent of mercury from the water, and the remaining elemental material is siphoned through a natural filtration system before the water is replaced in the reservoir.

“Essentially, we are taking out environmental hazards and replacing it with clean water,” Scherzinger said.

While the environmental portion of the project focuses on mercury, NID will also cull gold and marketable metals used in technology and will attempt to sell the collected gravel with an eye toward making the estimated $9 million project pencil out.

“Teichert is very eager to have the aggregate, and there is a market for elemental mercury,” Scherzinger said.

NID expects to pull at least $1 million worth of gold from Combie to defray costs.

While metal extraction comprises the near-term economic goals of the project, Scherzinger is cognizant that other water purveyors on the western slope face the same problems as NID.

Scherzinger said he could envision a time when NID rents the machine and/or lends its expertise.

It is estimated that about 50 to 150 pounds of mercury will be removed from the reservoir during the three- to five-year span of the project.

Following the completion of the mercury removal project at Combie Reservoir, NID will turn its attention to the much-larger Rollins Reservoir, upstream from Combie, Scherzinger said. The mercury machine will have to be scaled for the larger body of water, Scherzinger said.

NID has considered and planned the environmental restoration project since 2007.